This invention relates to a marine propulsion system, and more particularly to an assembly for facilitating construction of a counter-rotating propeller shaft assembly.
In a conventional marine propulsion system, a vertical input shaft is provided with a drive gear at its lower end, which meshes simultaneously with forward and reverse gears mounted for free rotation about the propeller shaft. A clutch assembly is provided for selectively coupling either the forward gear or the reverse gear to the propeller shaft, so that the desired direction of rotation is imparted to the propeller shaft for driving the boat either in a forward direction or a reverse direction.
In a conventional drive, the forward gear is disposed in the fore end of a propeller shaft cavity formed in the lower end of the gearcase. Forward thrust on the propeller shaft is transferred through the propeller shaft to the forward gear, which is supported by a bearing abutting an internal shoulder formed in the propeller shaft cavity. The forward thrust is transferred from the forward gear to the bearing, and from the bearing to the gearcase through the internal shoulder.
A counter-rotating, or lefthand rotation, drive system is typically provided in one of the drives of a dual drive installation. This way, the propeller torque from the conventional system and the propeller torque from the counter-rotating system substantially cancel each other.
In a counter-rotating system, the propeller blades are pitched oppositely from a conventional system. The gear in the fore end of the propeller shaft cavity is the reverse gear, and the rearwardmost gear is the forward gear. With this arrangement, the forward thrust imparted to the propeller shaft must be transferred to the gearcase at a point rearwardly of the forward gear. Thus, the forward and reverse gears must be supported independently of the propeller shaft.
To absorb forward thrust in the propeller shaft, a flange or the like is provided on the propeller shaft at a point rearwardly of the gear set. A bearing and carrier assembly is disposed between the flange and an inwardly projecting rib formed on the inner wall of the propeller shaft cavity, for transferring forward thrust to the gearcase.
It is desirable, of course, to utilize a single gearcase casting both for the conventional drive system and for the counter-rotating drive system. It is an object of this invention to allow use of a conventional gearcase having a conventional propeller shaft cavity in assembling a counter-rotating drive system.
Assembling the components of a counter-rotating system into the gearcase cavity presents a number of difficulties when an integral flange is formed on the propeller shaft. It is further an object of this invention to provide ease of assembly of the components of a counter-rotating drive system into the gearcase cavity.
In accordance with the invention, a marine propulsion system includes a depending gearcase having a rotatable shift shaft mounted thereto and a propeller shaft cavity disposed toward its lower end. A propeller shaft is disposed in the propeller shaft cavity, and is adapted to be rotatably driven by a drive shaft and forward and reverse gears disposed within the cavity, for rotating a propeller connected to the propeller shaft. The propeller shaft is provided with means for transferring forward thrust in the propeller shaft to the gearcase at a point aft of the rearwardmost of the forward and reverse gears. The invention comprises an arrangement for facilitating assembly of a shifting mechanism and one of the forward and reverse gears within the cavity. An adaptor member, including means for rotatably supporting and fixing the position of the fore one of the forward and reverse gears within the gearcase cavity, comprises means for mounting a movable shifting cam to the adaptor member. The adaptor member accomodates connection of the shift shaft to the shifting cam. Mounting means is provided for mounting the adaptor member within the gearcase cavity and fixing its position relative to the gearcase. In a preferred embodiment, the adaptor member comprises cup means for rotatably supporting the fore one of the forward and reverse gears and fixing its position within the gearcase cavity. A bearing member is adapted to be received within the cup means, and the gear is mounted to the bearing member. The adaptor member, bearing and gear can be assembled on the outside and pressed into the forward end of the gearcase cavity so that the adaptor member abuts an internal shoulder formed in the cavity. The adaptor member includes a passage for receiving the movable shifting cam. When the adaptor member is mounted into the gearcase cavity, the shift shaft is inserted through an opening provided in the adaptor member so as to engage the shifting cam. An upstanding tube is preferably provided on the adaptor member toward its forward end, and is adapted to be received between a pair of cast inwardly projecting internal ribs formed in the gearcase cavity. During insertion of the adaptor member into the gearcase cavity, the tube is received between the cast ribs and is crushed, simultaneously providing proper location of the adaptor member within the gearcase cavity and thereafter non-rotatably fixing its position relative to the gearcase.
The invention also comprises a method of assembling a counter-rotating drive arrangement within the propeller shaft cavity of a gearcase. In accordance with this aspect of the invention, a first gear is rotatably mounted to an adaptor member. The adaptor member is mounted to the gearcase toward the fore end of the gearcase cavity, so as to fix the position of the first gear within the gearcase cavity. A drive gear is mounted to the input shaft, which is rotatably mounted within the gearcase, with the drive gear engaging the first gear. A shift mechanism is assembled within the propeller shaft. A propeller shaft assembly with a second gear and the shift mechanism is then assembled into the gearcase cavity, with the second gear engaging the drive gear and the shift mechanism extending into the adaptor member. The shift shaft, which is rotatably mounted to the gearcase, is connected through an opening provided in the adaptor member to the shift assembly coupled to the propeller shaft assembly, which has been inserted into the adaptor member. The propeller shaft and second gear are then secured within the gearcase cavity.